Chemical Composition, Antibacterial Activity, and Synergistic Effects with Conventional Antibiotics and Nitric Oxide Production Inhibitory Activity of Essential Oil from Geophila repens (L.) I.M. Johnst

• Main Authors: Huijuanzi Rao, Pengxiang Lai, Yang Gao
• Format: Article
• Language: English
• Published: MDPI AG 2017-09-01
• Series: Molecules
• Subjects: Geophila repens (L.) I.M. Johnst; essential oil; GC-MS; antibacterial; synergistic; Checkerboard method; nitric oxide
• Online Access: https://www.mdpi.com/1420-3049/22/9/1561

Geophila repens (L.) I.M. Johnst, a perennial herb, belongs to the Rubiaceae family. In this study, we identified the chemical composition of the Geophila repens essential oil (GR-EO) for the first time. Totally, seventy-seven compounds were identified according to GC and GC-MS, which represent 98.0% of the oil. And the major components of GR-EO were β-caryophyllene (23.3%), β-elemene (8.0%), farnesyl butanoate (7.4%), myrcene (3.5%), and trans-nerolidol (3.3%). Then we evaluated the antibacterial activities of GR-EO and the synergistic effects of GR-EO in combination with commercial antibiotics using the microdilution and Checkerboard method. The results demonstrated that GR-EO possessed an excellent broad spectrum antibacterial activity, especially against Pseudomonas aeruginosa and Bacillus subtilis. It also showed that the combined application of GR-EO with antibiotics led to synergistic effects in most cases. And the most prominent synergistic effect was noticed when GR-EO was in combination with Streptomycin and tested against Escherichia coli (fractional inhibitory concentration indices (FICI) of 0.13). Additionally, the results of a Griess assay revealed that GR-EO exhibited a potent inhibitory effect on NO production in lipopolysaccharide (LPS)-activated RAW 264.7 (murine macrophage) cells. In conclusion, the combination of GR-EO and the commercial antibiotics has significant potential for the development of new antimicrobial treatment and reduction of drug resistance.